The present invention relates generally to a vehicular transmission which comprises a speed change mechanism and a main clutch (also referred to as xe2x80x9cstarting clutchxe2x80x9d) and which controls mechanical power transmission from an engine with speed change control performed by the speed change mechanism and the main clutch.
Such vehicular transmissions have been used for mechanical power transmission in vehicles. As speed change mechanisms incorporated in these transmissions, not only gear transmissions with a plurality of speed ratios but also continuously variable transmissions with a belt, etc. have been used for speed change control. Recently, a hybrid transmission which uses an electrical motor in addition to an engine has been introduced for fuel efficiency. The applicant of the present invention is also developing a hybrid transmission. This hybrid transmission comprises a continuously variable transmission with a metal V-belt which is disposed around the common output shaft of an engine and an electrical motor arranged in series, and the output shaft of the continuously variable transmission is provided with a forward/reverse switching mechanism and a starting clutch (main clutch).
One purpose for developing this transmission is to improve fuel efficiency. Therefore, there is a consideration that the operation of the engine be controlled such that it stops when the vehicle has stopped (referred to as xe2x80x9cidling eliminationxe2x80x9d). As such idling elimination control, there is a method to stop the engine when the engine comes into idling after the vehicle has stopped completely. However, when the vehicle is decelerated by releasing the accelerator pedal that has been depressed, an engine brake is effected. It is known that, during this deceleration, the fuel injection to the engine is terminated (or the supply of fuel is terminated). In this situation, there is a more desirable way to eliminate engine idling. When the vehicle is decelerated to a halt, the fuel injection is terminated, so this condition should be maintained to stop the engine. This method seems more favorable for improving the fuel efficiency.
However, this idling elimination, which involves termination of the fuel injection, is likely to experience the following problem. If the vehicle is stopped while the starting clutch is in engagement, then the rotational resistance of the engine is so great that the vehicle is decelerated too rapidly for the passengers to be comfortable at the stopping. This deteriorates the riding quality of the vehicle. One cause of this problem is the control executed for changing the speed ratio of the transmission to a LOW ratio when the vehicle is to be stopped. This shifting to the LOW ratio just before the halt of the vehicle makes the effect of the engine brake remarkably strong. On the other hand, if the starting clutch is released when the engine is allowed to stop, then no engine brake can be achieved, which also reduces the riding quality of the vehicle.
It is an object of the present invention to provide a control system for a vehicular transmission which system eliminates engine idling without impairing riding quality when the vehicle decelerates and stops after fuel supply termination.
In order to achieve this objective, the present invention provides a control system for a power transmission which is used for driving a vehicle. This power transmission conveys the driving force of an engine through a speed change mechanism (for example, the continuously variable transmission CVT of the embodiment described in the following section) and a main clutch (for example, the starting clutch 5 of the following embodiment). The speed change mechanism performs a speed change, and the main clutch is used to turn on and off of the transmission of the driving force. In this power transmission, while the vehicle is being decelerated for a halt, the control system terminates the fuel supply to the engine for decelerating the vehicle, releases the main clutch gradually under predetermined conditions, and then stops the engine so as to bring the vehicle into a halt.
According to the present invention, while the vehicle is being decelerated by the termination of the fuel supply to the engine, if the predetermined conditions are satisfied, the main clutch is released gradually, and then the engine is stopped to bring the vehicle into a halt. Therefore, an engine brake effected in the deceleration is controlled to lessen gradually, and the vehicle is stopped without engine idling. In this way, not only an engine brake is effected appropriately, but also the passengers in the vehicle can sense a feel of idle running at the time of the vehicle coming to a halt. Thus, the present invention achieves for an idling elimination control as good a drive quality as that of the drive control which is executed for decelerating and stopping the vehicle without any idling elimination control.
As the above mentioned predetermined conditions, the following conditions are considered: the brake of the vehicle is being operated, the speed of the vehicle has become equal to or lower than a predetermined speed, the reduction ratio of the speed change mechanism has come to be almost at a LOW ratio, and the throttle of the engine is essentially closed. When all the conditions are satisfied, the control system releases the main clutch gradually and then stops the engine to bring the vehicle into a halt. In other words, after the driver releases the accelerator pedal and steps down the brake pedal to decelerate the vehicle, when the speed of the vehicle becomes equal to or lower than a certain low speed (for example, 15 km/h) and the speed change ratio becomes almost a LOW ratio, the main clutch is controlled to be released gradually to achieve a good drive quality for the deceleration as described above.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.